Publication Date

Summer 2023

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Moss Landing Marine Laboratories

Advisor

Maxime Grand; Luke Gardner; Michael Graham

Abstract

Feeding ruminant livestock seaweed rich in bromoform (CHBr3) is an emerging strategy to reduce methane emissions from the livestock sector to meet climate targets. Consequently, there is a strong interest in farming bromoform rich seaweeds (e.g., Asparagopsis taxiformis) on a large scale which may impact the atmospheric inventory of bromine and in return induce catalytic ozone destruction. However, to date, only three studies have measured bromoform emission rates from Asparagopsis seaweeds which vary by order of magnitude. To fill this gap, the most comprehensive data set of bromocarbon emissions from A. taxiformis, a leading candidate for enteric methane reduction in cattle, was collected from Santa Catalina Island (California) under natural conditions, where the measured emissions were found to be five to twenty times higher than previously reported values. Bromocarbon emission data were also collected from Gracilaria parvispora, which has methanogenic reduction potential and is part of the globally cultivated Gracilara genus. Light intensity and water temperature most affected bromocarbon emission rates for both seaweed species. A comparison of emissions rates between aquaculture tanks (380 L) and bottle incubations (0.5 L) suggests that bottle incubations can represent of aquaculture settings. Finally, this study suggests that mass-producing A. taxiformis for approximately 50% of Californai cattle at a 1% inclusion rate (dry weight) is unlikely to significantly increase annual global bromocarbon emissions, whereas mass producing A. taxiformis for approximately 26% of all United States cattle may significantly increase global bromocarbon emissions.

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